@shri,
Labour department will handle cases of overseas employment by a hk based office. In a case such as this an employment visa is not required for hk if employment is outside of hk but can still have legal jurisdictions in Hong Kong. There are some cases of hk residents working in China for a hk company able to successfully claim unpaid wages in Hk courts from hk office.
To the OP,
Proper channel is the labour department. Need to go in person unfortunately and possibly quite a few times if it goes to court. Usually after the initial complaint the employer will settle. Not paying wages is an offence with a short jail term and fine. You can insist an investigation be opened into the matter on your in person visit to the labour department. You go to the particular department based upon your hk office location. There's no cost at the labour department and relatively no cost to you if you go to the tribunal. (couple hundred hkd). If you suspect they are winding up then proceed to file complaint immediately. Hk has minimal insurance to cover you.
One of the key points is that you signed no settlement and objected in writing to any shortfalls in your payment. Best to call the labour department to learn your full entitlements by law and how to calculate it. Annual leave, how to calculate wages (including average bonus and commissions), etc.
A lawyer is not worth it in my opinion but if you went all the way then you could recover "some" costs, flying to hk, basic hotels, transport, food, lost wages, etc. I would hire a lawyer (costs I think would amount to greater than US$2k to write a couple letters and quickly escalates) if the amount was over hk$1m but the legal system in Hk is quite strong and the court will help you to make and write the complaint, they hold your hand basically. The company director could be personally liable for such a case and hence usually is solved albeit you may accept a discount. In the case of not paying your wages when due the ball is in your court and I would not settle. The employer has to answer for breaking the law with personal penalities. If you settle then likely the case would be done and not proceed to prosecution since no one was found guilty by the court.